Ask HN: One startup at a time?

I have a friend who's asked me to work on a startup with him and several others. They have secured 10s of thousands for this new venture. The idea seems ok but nothing has been executed yet.. Just a lot of talk basically at this point.

I have also been working on another web startup that is about to go into public beta within 1-2 months. That startup has no funding, but it does have a nearly finished and well fleshed out product with a few private beta users already and it's only 2 founders instead of 5 or 6 which the other one has.

My friend has indicated that I would only be involved part-time but I am the most technical guy on the team so I know my involvement would probably require a lot more than that and as anyone who's done a startup knows - it ain't easy..

It's tempting of course b/c of how well funded they are but it would be really hard for me to distract myself from something that I put a year of my life into and is nearly finished. I also realize how great a divide there is between talking about building a product and actually building a product even if you're well funded.

I wanted to know if anyone out there has had a similar experience and/or has been successful dividing their time between 2 or more startups or if you think the idea of doing multiple startups at a time is just plain crazy.. What would you do?

thanks